The present invention generally relates to an embedded microelectronic capacitor and a method for fabrication and more particularly, relates to an embedded microelectronic capacitor that is equipped with geometrically-centered electrodes and a method for fabricating such capacitor.
In the development of modern technology for wireless communication, for digital computing equipment, for portable consumer electronics, the requirements for high frequency, wide band and miniaturization are most critical and must be met. One of the modern trend in such development is centered on the use of embedded components in order to reduce real estate occupied by such circuits. For instance, it is desirable for a circuit designer to replace a most commonly used component of a capacitor in a surface mount technology with an embedded capacitor. This can be achieved by utilizing various structures or materials to fabricate the embedded capacitor. However, when various different fabrication methods are used to embed a capacitor, the connection between the embedded capacitor and other circuit components frequently produces parasitic effects, thus adversely affect the electrical characteristics of the capacitor. The parasitic effect becomes worse as the frequency of the capacitor becomes higher. In the worst case, the capacitor characteristics can be affected to such a stage that it exhibits the characteristics of electrical inductance. The threshold frequency for such transition in characteristics is known as the self-vibration frequency of the component. In modern digital or analog circuits, design of the circuit is more desirably high frequency and wide band. The characteristics of the component that function under high frequency becomes even more important. It is therefore highly desirable to improve the electrode connection method in an embedded capacitor in order to increase its self-vibration frequency for use in high frequency circuit applications.
Conventionally, as shown in U.S. Pat. No. 6,191,934 entitled xe2x80x9cHigh Dielectric Constant Embedded Capacitorsxe2x80x9d, the connection method for the embedded capacitor is by edge connection. For instance, as shown in FIG. 1 of the patent, each electrode plate 14 is connected on the edge by a trace 16 wherein the terminal of the trace 16 is formed in a connecting pad 12. A series of connecting pads 12 are then electrically connected together by a lead 18 providing electrical connection for the embedded capacitor 10 to outside circuit components.
A disadvantage of the edge connection shown in FIG. 1 for the embedded capacitor 10 is that not only circuit real estate is increased due to the area occupied by trace 16 and by the connecting pads 12, the edge connection also produces unavoidable and difficult-to-analyze effective parasitic elements. As a result, the high frequency electrical characteristics of the embedded capacitor are severely affected to decrease the self-vibration frequency and to thus make such connection method inadequate in high frequency circuits.
In another conventional method for connecting embedded capacitors, as shown in U.S. Pat. No. 5,400,210 entitled xe2x80x9cSubstrate Having a Built-In Capacitor and Process for Producing the Samexe2x80x9d, through via 22 is utilized in an embedded capacitor 20 for connecting to the positive and negative electrode plates. The point of connection is far away from the geometric center of the electrode plate and thus causing unbalanced high frequency effective circuit due to the variation in the distances between the connection point and the edges of the electrode plates. Such unbalanced high frequency effective circuit further deteriorates the high frequency electrical characteristics of the embedded capacitor such as its self-vibration frequency.
It is therefore an object of the present invention to provide a method for connecting an embedded capacitor without the drawbacks or shortcomings of the conventional connection methods for such embedded capacitors.
It is another object of the present invention to provide a connection method for embedded capacitors such that its self-vibration frequency can be improved.
It is a further object of the present invention to provide a connection method for embedded capacitors such that the capacitor can be utilized in high frequency circuits.
It is still another object of the present invention to provide a connection method for embedded capacitors such that the connection point is within 50% of the diameter of the electrode plate from its geometric center.
In accordance with the present invention, an embedded microelectronic capacitor equipped with geometrically-centered electrodes and a method for fabricating such capacitor are provided.
In a preferred embodiment, an embedded microelectronic capacitor is provided which includes an upper electrode plate of a first polarity; a middle electrode plate of a second polarity opposite the first polarity of the upper electrode plate and having a center aperture therethrough; at least one lower electrode plate of the first polarity in electrical communication with the upper electrode plate through a center via positioned through the center aperture of the middle electrode plate without shorting to the middle electrode plate, the center via is positioned at a distance from a geometric center of the middle electrode plate not larger than 50% of a diameter of the at least one lower electrode plate; and a first electrical lead connected to an edge portion of the upper electrode plate wherein the upper electrode plate, the middle electrode plate and the at least one lower electrode plate are embedded parallel to each other in at least one dielectric material forming at least a single-port capacitor.
The embedded microelectronic capacitor may further include a second electrical lead connected to an edge portion of the middle electrode forming a dual-port capacitor. The middle electrode may be grounded forming a single-port capacitor. The upper electrode plate, the middle electrode plate and the at least one lower electrode plate are fabricated of an electrically conductive metal. The upper electrode plate, the middle electrode plate and the at least one lower electrode plate may be fabricated of Cu or Al. The center via, the first electrical lead and the second electrical lead may be formed of a low electrical resistance metal, or may be formed of tungsten. The upper electrode plate, the middle electrode plate and the at least one lower electrode plate each has a thickness between about 0.01 mm and about 0.1 mm. The upper electrode plate, the middle electrode plate and the at least one lower electrode plate are embedded parallel to each other at a distance between about 0.05 mm and about 0.5 mm.
The present invention is further directed to an embedded microelectronic capacitor which includes a first electrode plate that has a first via mounted perpendicularly therethrough making electrical connection and an oppositely positioned first aperture in the plate adapted for receiving a second via without making electrical connection; at least one second electrode plate that has a second aperture therethrough adapted for receiving the first via without making electrical connection and a second via mounted perpendicularly therethrough making electrical connection with the at least one second electrode plate but not with the first electrode plate, the at least one second electrode plate is substantially parallel to the first electrode plate; the at least one third electrode plate that has the first via mounted perpendicularly therethrough making electrical connection and an oppositely positioned third aperture adapted for receiving the second via without making electrical contact, the at least one third electrode plate is substantially parallel to the second electrode plate; and a dielectric material filling a gap formed in between the first electrode plate, the at least one second electrode plate and the at least one third electrode plate.
In the embedded microelectronic capacitor, the first via is mounted through the first electrode plate off-centered in the first electrode plate. The second via is mounted through the second electrode plate off-centered in the second electrode plate. The first electrode plate, the at least one second electrode plate and the at least one third electrode plate are fabricated of an electrically conductive metal, or fabricated of Cu or Al. The first via and the second via may be formed of a low electrical resistance metal, or may be formed of tungsten. The first electrode plate, the at least one second electrode plate and the at least one third electrode plate each has a thickness between about 0.01 mm and about 0.1 mm. The first electrode plate, the at least one second electrode plate and the at least one third electrode plate are embedded parallel to each other at a distance between 0.05 mm and about 0.5 mm.